Rotor blades of an axial flow fan are swept forward in the rotation direction and tilted frontward toward the upstream side of a suction airflow mainly to reduce noise, and also outer diameters and chord length of the rotor blades are enlarged within the limit of product size, to increase air capacity and static pressure.
As described above, when adopting a shape aimed for larger air capacity and higher static pressure as well as noise reduction, a blade is often formed into a shape such that stress concentrates in the base of the leading edge of the blade. However, strength to withstand wind drifts and gusts also needs to be secured.
Conventionally, there has been an axial flow fan (see Patent Literature 1, for example), in which the plate thickness of the stress-concentrating part as described above is varied to avoid concentration of stress.
Additionally, there has been an axial flow fan (see Patent Literature 2, for example), in which a part of a leading edge portion of a vane closer to a boss portion than an arbitrary point on the leading edge portion of the vane is extended in the rotation direction, as if the part of the leading edge portion of the vane on the boss portion side is continuous. Thus, concentration of stress can be avoided without locally increasing the thickness of the blade near the boss portion.